A health and safety charge against rail maintenance company Jarvis over the 2002 Potters Bar train crash has been dropped.
Six passengers and a pedestrian were killed in the Hertfordshire crash when a London to Kings Lynn train derailed over a faulty set of points.
Last November, the Office of Rail Regulation (ORR) brought a charge under the Health and Safety at Work Act against Jarvis, which was the maintenance contractor at Potters Bar at the time and which is now in administration.
Today, the ORR said: "While there remains sufficient evidence to provide a realistic prospect of conviction of Jarvis, a prosecution would no longer be in the public interest."
Overall responsibility for rail maintenance at the time of the crash on May 10 2002 lay with Railtrack, which was replaced by Network Rail (NR) later in 2002.
When charging Jarvis last autumn, the ORR also bought a similar charge against NR, which pleaded guilty to the charge at Watford Magistrates' Court last month.
The next hearing of the proceedings against NR will take place at St Albans Crown Court on March 30, when a provisional date for the sentencing of Network Rail should be set.
Giving reasons for its decision not to proceed with the prosecution of Jarvis, the ORR said there were a number of factors, including:
:: The changed nature of any future trial - Jarvis's administrators have advised that they would take no part in any proceedings, while NR has pleaded guilty. Under these circumstances, continuing proceedings against Jarvis would mean that any trial would be of Jarvis alone;
:: A trial of Jarvis alone would be lengthy, costly, and if convicted lead to only a small financial penalty and delay the conclusion of the proceedings against NR;
:: Members of the victims' families expressed the view that there was little value in continuing the prosecution.
One of those killed in the crash was Austen Kark, 75, who was travelling with his wife, author Nina Bawden, now 86, who was badly injured.
Their daughter Perdita Kark said today: "It's an appalling thing for the families involved that this has all taken so long.
"We have had to battle and battle and battle to get this far. Jarvis effectively no longer exists."
She went on: "What's important now is that Network Rail ensures the railways are as safe as they can be.
"Since Potters Bar there have been some areas in which safety has improved but there is more to be done."
In 2005, the Crown Prosecution Service said there was no realistic prospect of conviction for gross negligence manslaughter against any individual or corporation in relation to the crash.
As well as the seven deaths, the crash resulted in injuries to more than 70 passengers.
An inquest jury concluded last year that a set of unsafe points on the track outside Potters Bar station caused the derailment.